1. Field of the Invention
The present invention relates to a zoom lens which is suitable for use in a TV camera, a video camera, a still camera and a digital camera, in particular to a small, light-weighted zoom lens which has excellent performance with good chromatic aberration characteristics at the telephoto end, while having a high zoom ratio higher than 15. The present invention also relates to an image pickup apparatus having such a zoom lens.
2. Description of the Related Art
Heretofore, there have been developed many zoom lenses composed of four lens units including in order from the object side a first lens unit having a positive refractive power which does not move for zooming, a second lens unit having a negative refractive power for varying magnification, a third lens unit having a negative refractive power for correcting image plane variation due to the varying of the magnification, and a fourth lens unit having a positive refractive power which does not move for zooming.
Japanese Patent Application Laid-Open Nos. 2004-109993 and 2009-037036 disclose as numerical embodiments zoom lenses having a high zoom ratio as high as 18 to 21 and an angle of field not smaller than 55 degrees and smaller than 75 degrees at the wide angle end. However, in the zoom lenses disclosed as numerical embodiments in Japanese Patent Application Laid-Open Nos. 2004-109993 and 2009-037036, the dispersion of the positive lenses in the first lens unit is not small and the refractive index thereof is not sufficiently high, resulting in insufficient correction of aberrations at the telephoto end and failing to achieve high performance and small size at the same time.